AN investigation is under way to discover what caused a major power failure at Monckton Coke and Chemical plant.

Black smoke and flames were seen pouring out of the chimneys on Monday but it is not known what caused the failure.

Environment manager Richard Cooper told the Chronicle: "The whole plant lost power but as to the reason why we don't know and will be investigating."

A spokesman for Hargreaves, owners of the plant, said because the continuous process was interrupted, smoke and other residues needed to be released to keep the plant operating safely and that the flames were part of a controlled release.

Fire crews were briefed by Monckton management and stayed only 15 minutes until they were satisfied there was no danger of fire or explosion.

Royston station manager, Jon Parkes, said a system fault caused loss of power on the exhaust system and they had been assured the fumes were not toxic.

The spokesman said the Environment Agency and Monckton management were conducting an investigation.

The spokesman added: "Until these investigations are completed we cannot respond to speculation as to the cause. We can confirm, however, that at no stage was there any danger to our employees on site or to local residents".